Proteomic profiling of plasma extracellular vesicles reveals a therapeutically targetable liver-heart axis in cardiac transplantation.

Extracellular vesicle-mediated interorgan communication represents a promising frontier in transplant immunology; however, its role in cardiac allograft rejection remains poorly characterized. We performed proteomic profiling of plasma-derived extracellular vesicles in a rat heterotopic heart transplantation model and identified a distinct liver-predominant protein signature during acute rejection, with antithrombin III (ATIII) emerging as a top candidate. Functional validation revealed that pharmacological extracellular vesicle inhibition intensified systemic and intragraft inflammation, whereas adeno-associated virus-mediated silencing of hepatic ATIII directly accelerated allograft rejection. Conversely, adeno-associated virus-mediated hepatocyte-specific ATIII overexpression attenuated rejection pathology, reduced immune cell recruitment, and markedly prolonged median graft survival. This protective effect was achieved without evidence of coagulopathic complications, indicating an immunomodulatory mechanism beyond ATIII's canonical anticoagulant function. Mechanistically, ATIII overexpression was associated with upregulation of heme oxygenase-1 (HO-1) in the liver and suppression of proinflammatory cytokine expression in the graft. These findings highlight hepatocyte-derived extracellular vesicles as important mediators of a liver-heart signaling axis in transplant rejection and further implicate the protein ATIII as a contributor to this axis. Our study reveals a therapeutically targetable liver-heart signaling axis in transplant rejection, whereby enhancing liver-derived ATIII or its downstream pathways (such as HO-1) could attenuate acute cardiac allograft rejection.